This invention relates to liquid-inflated, liquid damming protective banks for damming liquids such as water, and is useful for flood control, water diversion, and the de-watering of construction sites; the protective bank being secured to the ground by adapted hydrostatic pressure of the surrounding or dammed water.
Floods are a common life threatening and property damaging occurrence, and the response to a flood is often an attempt to contain, divert or in some way control the flood water, usually by hastily constructing earthen dikes or by manually building barriers of sandbags. These methods have disadvantages.
Constructing barriers of earth requires the use of suitable heavy equipment that must be transported to the flood locale. Building earth dams with this equipment is time consuming and very expensive. Additionally, earth must be excavated, leaving scars and pits on the ground, and the dikes constructed erode easily into the flood water, thereby polluting the water and eventually failing. The sandbag method is very labor intensive and time wasting. These difficulties usually result in flood protection that is ineffective and too late, and necessitate repair of damage and removal of sandbags once the flood waters recede.
It is sometimes necessary to accomplish construction work in areas covered by water, consequently requiring the de-watering of the site. Conventional methods used to achieve this goal are to build dams using on-site soils, or installing sheet piling. Again, earth constructed check dams erode into waterways, causing the siltation of fish spawning beds and other environmental damage. Sheet piling is both labor and capital-equipment intensive. Further, such barriers are difficult to remove after the project is completed. When very large areas must be de-watered, both of these methods are impractical.
With the purpose of obviating the disadvantages associated with earth banks, sandbag protective banks, and sheet piling dams, other methods have been developed, the simplest and most efficient of which include the use of portable barriers, in the form hose-like tubes or casings which may be stored, handled, and transported in a collapsed state and filled with liquid, usually water, at the location where they are to be used. There are numerous examples of such water-filled dams disclosed in literature and patents.
The book "Tensile Structures" (1962), shows a single large hose of tough fabric which can be placed on endangered dikes. This hose is filled with water to control flooding. There is a problem with this type of design: a single tube of water that is freestanding, i.e., non-restrained, has a tendency to roll due to forces of water pressure, wave action and/or slope. A solution to the problem is a multiple tube dam. When inflated, multiple tube dams have a form that is stable. The same book shows a drawing of freestanding multiple bags. The water-filled, flexible and impermeable bags are joined in a side-by-side relationship (p144, 145). Freestanding, water or liquid-filled dams are also disclosed in U.S. Pat. No. 4,692,060, U.S. Pat. No. 4,799,821, U.S. Pat. No. 4,981,392, U.S. Pat. No. 5,040,919, U.S. Pat. No. 5,125,767, U.S. Pat. No. 5,645,373, U.S. Pat. No. 5,785,455, and U.S. Pat. No. 5,865,564.
A significant advantage of such hose casings is that they are diminutive in a deflated state, and therefore conveniently stored until they are needed, at which time they can easily be transported to the installation site. The anchoring liquid, ordinarily water, with which they are to be filled is usually abundant on-site. Consequently, a large number of these dams may quickly and efficiently be installed in place and activated by simply inflating them with the very same water they are controlling. Another advantage is that minimal site preparation is required for their successful use.
One thing that these portable damming devices have in common, is that the member of the protective bank abutting against the surface, abuts against the same over its entire area in the commendable objective of achieving the biggest possible tightness against the surface. Thus, these structures originate from the basic idea that the larger the area of contact against the surface, the more reliable becomes the sealing off of leakage under the protective bank. The above listed patents in every case use the surface abutting water-inflated barrier member(s) to prevent dammed liquid from leaking under the protective bank, although in some instances, skirts are used to assist toward this objective (see, e.g., U.S. Pat. No. 5,645,373).
Prior art teaches that freestanding, water-filled dams achieve stability because of the geometry of the dam, and they are stable against rolling so long as the level of water being controlled by the dam is not too high. As the dammed water level rises, there is a buoying force that causes the stabilizing portion of the dam to lose weight, until the dam fails by rolling, sliding, losing water underneath, or a combination of these modes of failure. These dams will fail before the height of the water dammed can reach the top of the dam. U.S. Pat. No. 4,981,392 teaches that the height of the dam must exceed the depth of water to be dammed, typically by a factor of one-third, to provide adequate vertical force to keep the structure in place in spite of the buoying force of the water contained. This portion of the dam extending above the water level, also known as freeboard, adds vertical weight, and is necessary to keep the above mentioned water-filled dams weighted to the surface.
Freeboard is essential or failure will result. Persons with experience in the art are familiar with freestanding, water-filled dam failures. Dam failure can mean the loss of an expensive dam, and the resulting flood water can cause considerable damage and put lives at risk. Also, a massive failed dam, rolling and sliding down a river, is a real danger to workers caught in its path.
U.S. Pat. No. 5,857,806 (the '806 patent) of Melin aims at obviating the above-mentioned disadvantages of the previously known protective banks. This patent teaches that the protective bank is assured a continuous anchoring ability, provided that drainage means are inserted between the surface and the member of the bank which abuts against the same, guaranteeing that the area of contact between the member and the surface is kept partially "dry" or at atmospheric pressure.
This dry area is therefore not affected by the buoying force of the dammed water. The drainage means in the '806 patent include mats and boards having channels and voids, and are attached to the barrier or are inserted between the bottom of the barrier and the surface. Although this patent demonstrates a praiseworthy advancement in the art, there are numerous problems associated with the disclosures.
Drainage mats and boards can become clogged with silt and other sediments. When this occurs, the dam of the '806 patent is affected by the same destabilizing buoyancy as the other previously listed dams. Mats and boards must be aligned perfectly to function properly, and are impossible to realign once the dam is inflated. Mats and boards would be time-wasting to install, add significant expense to the dam, and require additional storage and transportation requirements. These drainage devices would make deployment of a dam across standing or moving water difficult or impossible. Mats and boards applied as separate devices would be removed after the dam is removed, and removal might be difficult as they would likely be under water and/or embedded into substrate surface sediments. The mats and boards would be difficult to clean because the channels, voids and porosity retain dirt and contaminants. The boards are described variously as stiff and rigid, which would mean that in a case where they are fastened to the dam, the dam could not be folded or rolled, and therefor nigh impossible to handle. The mats are described as having a thickness with layers and channels, and these devices would also be difficult to roll or fold.
The '806 patent teaches that there must be a dry side toward which flood liquid leakage is drained in order to achieve near atmospheric pressure under the dam, and the resulting hydraulic, i.e., hydrostatic, pressure differential necessary for stabilizing the dam. This dam has no provisions that would allow it to function as a pressure secured dam should there be significant water levels on both sides of the dam.
Finally, the type of liquid damming protective bank as described in the '806 patent requires that two conditions be fulfilled in order for the dam to function properly: (1) a sealing means on the flood-side edge of the dam, and (2) a leakage draining means under the dam. By itself, an effective seal that stops all or most of the leakage under the dam, along with the inherent natural drainage in these liquid anchored dams, will result in the desired pressure differential and ensuing stability of the dam. But a draining means also requires a sealing means in order for the dam to perform as intended. Certainly, a draining means without a sealing means could not function as this type, or any type of dam, because the whole idea of a dam is to prevent water from flowing through or under the dam. Although the '806 patent shows an example of a sealing device, this sealing layer offers nothing novel to improve this basic function, i.e., sealing of leakage, which is a necessary requirement in a dam. U.S. Pat. No. 5,470,177 and U.S. Pat. No. 4,799, 821 describes the use of similar packing materials to prevent leakage. One thing the previously known sealing methods have in common, whether it is a seal layered beneath an anchoring barrier as described in the two patents above, or a sealing skirt, as in U.S. Pat. No. 5,645,373, is that the sealing member is brought to abut against the surface over its entire area in the praiseworthy purpose of obtaining the best possible seal. What actually happens though, is numerous points of sealing that are in a broken line, and are spread out at various places behind the flood side edge of the seal. Whether it is hydrostatic pressure forcing a skirt to the substrate surface, or the anchoring weight of a water-filled barrier, the seal will not improve and a moderate amount of leakage will flow around these scattered points of sealing. Because there is some sealing effectiveness over the entire width of the seal, from the flood side of the seal to the "dry" side of the seal, hydrostatic pressure will increase between the seal member and the substrate surface, and the seal will be buoyed up, resulting in a further decrease in sealing effectiveness.
There are other problems with the seal described in The '806 patent. The sealing means described is layered under the flood side edge of the barrier member, and therefore is inaccessible should it leak and need improvement. Also, this seal will allow increased leakage as a result of increased dammed water levels, and, like the aforementioned mats and boards under the protective bank, the applied seals have the very same disadvantages as the mats and boards in respect to installation, removal, cleaning, transportation, storage, and cost.
U.S. Pat. No. 5,460,462 and U.S. Pat. No. 4,582,451 describe seals constructed of an elastomeric, i.e., stretchable membrane, intended to the seal the periphery of flood gates, and these seals are designed to be held in position by hydrostatic pressure loading of a dammed liquid. The purpose of these seals is to stop leaks for the sake of obstructing water flow through the flood gates, with the intention of preventing water damage. The are not intended to be used for the sake of reducing hydrostatic pressure to stabilize a supporting barrier member. Also there is no mention of an edge sealing means on these membrane seals that further increases their effectiveness.
U.S. Pat. No. 4,184,788 shows devices for draining fluid from beneath an erosion control structure to equalize the hydrostatic pressure developing between the form and the surface upon which the form rests. The draining means described in this patent are applied mats of porous materials, and pipes. The above patent also teaches an embodiment with a skirt, but the skirt or apron is intended to prevent undercutting or scour of the form, and not as a sealing device.
Suction anchors making use of pump suction to induce hydrostatic differential pressure have been used to anchor pilings, storage vessels, and drilling devices to an underwater substrate surface, shown for example in U.S. Pat. No. 3,965,687 and U.S. Pat. No. 4,572,304. There is no reference made to using these suction anchors to stabilize and secure a protective bank damming device to the substrate surface.